Monitoring Usage of Telecommunications Services

1. A method of generating a call detail record for usage of a telecommunications service established between telecommunications networks, comprising the steps of: monitoring messages in a signalling system for co-ordinating operation of a first telecommunications network and a second telecommunications network and carried over signalling links in the signalling system between a service switching function (SSF) entity in the first telecommunications network and a service control function (SCF) entity in the second telecommunications network; selecting messages that relate to instances of usage of a telecommunications service initiated by the SSF entity to a signal switching point (SSP), to yield selected messages; correlating the selected messages in accordance with the instance of usage to which the selected messages relate, to yield correlated selected messages; and using information in the correlated selected messages to derive a call detail record for the instance of usage of the telecommunications service.

2. The method of claim 1 , wherein the signalling system uses Signalling System No. 7 protocols and the selected messages are Transaction Capabilities Application Part (TCAP) messages.

3. The method of claim 2 , wherein said correlating of the TCAP messages is performed in accordance with transaction identifiers and identifications of origin and destination of the TCAP messages.

4. The method of claim 1 , wherein the telecommunications service provides telecommunications facilities to a mobile telecommunications device.

5. The method of claim 4 , wherein the first telecommunications network comprises a home telecommunications network with which the mobile telecommunications device is associated, and the call detail record to be generated relates to usage of the telecommunications service via a visited telecommunications network other than the home telecommunications network.

6. The method of claim 5 , wherein the selected messages are exchanged between the visited telecommunications network and the home telecommunications network, and relate to at least one of (a) requests from the visited telecommunications network to the home telecommunications network for instructions on handling service usage originated by the mobile device, or (b) service usage established in response to such instructions.

7. The method of claim 1 , wherein the telecommunications service comprises a service selected from the group consisting of a voice service, a data service and a message service.

8. The method of claim 1 , wherein said information is carried within the correlated selected messages in accordance with a protocol additional to a protocol used for assembling the correlated selected messages, said information relating to exchange of data between the SSF entity and the SSP.

9. The method of claim 1 , wherein the SSP is located in a third telecommunications network.

10. Apparatus for generating a call detail record for usage of a telecommunications service established between telecommunications networks, comprising: a monitor for monitoring messages in a signalling system for co-ordinating operation of a first telecommunications network and a second telecommunications network and carried over signalling links in the signalling system between a service switching function (SSF) entity in the first telecommunications network and a service control function (SCF) entity in the second telecommunications network; a message selector for selecting messages that relate to instances of usage of a telecommunications service initiated by the SSF entity to a signal switching point (SSP), to yield selected messages; a correlator for correlating the selected messages in accordance with the instance of usage to which the selected messages relate, to yield correlated selected messages; and a call detail record generator for using information in the correlated selected messages to derive a call detail record for the instance of usage of the telecommunications service.

11. The apparatus of claim 10 , wherein the SSP is located in a third telecommunications network.